As far as I have managed to see many time many webmasters use several domains for the same website. But it is not clear me for which purposes the same website has to be available under different domains? What benefits can be taken from multiple domains?

the main advantages are keyword domains, so for example if your primary search term you are targeting is "holidays in france" then the domain holidaysinfrance.com will get you a good rating without too much work, but you may also want to target the search term "vacations in france" so registering the domain vacationsinfrance.com will help get you better rating for that search term also.

What benefits can be taken from multiple domains?

There is NO benefit at all, Search engines will eventually figure out they are all the same and filter out the ones that are less "important"

There is however a very big DISADVANTAGE and that is you are splitting the potential links between several mirrors.

There is NO real "advantage" in "keyworded domains" it is a total myth.

if you have more than 1 domain free that can apply i would say go for it. But if your considering buying another domain for it, stick with the one youve got

All i see that it does is gives the users of the site more names to use to go to the webpage...

Each domain name (if that is good domain name of course)have direct traffic. That is being made in hope for direct traffic for the domain name and redirection it to the main domain.

Originally Posted by GamingFreak

All i see that it does is gives the users of the site more names to use to go to the webpage...

So does doing it properly and 301 redirecting all the other names to ONE. And there you don't have the search engine disadvantages.

Originally Posted by chrishirst

So does doing it properly and 301 redirecting all the other names to ONE. And there you don't have the search engine disadvantages.

But another domain names will be ignored by SE.

Originally Posted by SiberForum

But another domain names will be ignored by SE.

Correct

Originally Posted by chrishirst

There is NO benefit at all, Search engines will eventually figure out they are all the same and filter out the ones that are less "important"

There is however a very big DISADVANTAGE and that is you are splitting the potential links between several mirrors.

There is NO real "advantage" in "keyworded domains" it is a total myth.

I see some advantage only if you bought various expired domains with some residual traffic of the same subject and point all them to the same site

Or, mabey one plans on making them into mini sites in the future and just has them redirecting for now to there major bread winner. Also, it becomes a sort of monopoly when you are the owner of many different, yet similar, names in your niche.

I don't see any benefit at all. If anything use the domain to develop another site

Originally Posted by pete.whiteside

I don't see any benefit at all. If anything use the domain to develop another site

Yes, I fully agree with you pete.whiteside!